Composite Substrate with Protective Layer for GaN Epitaxy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current GaN-based semiconductor devices face issues with lattice mismatch, thermal stress, poor thermal conductivity, and high cost due to the lack of suitable substrates for epitaxial growth, leading to degraded crystal quality and limited application in optoelectronic devices.
Innovation Solution
A composite substrate with a thermally and electrically conductive layer and a GaN mono-crystalline layer, partially clad with a protective layer to prevent metal diffusion, enabling homoepitaxy and reducing production costs, while allowing for vertical structure LED formation and improved crystalline quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sapphire substrate is used for GaN epitaxial growth, then the substrate is widely available and easy to manufacture, but the large lattice mismatch and thermal stress produce high concentration of dislocations that degrade GaN crystal quality
Solution Approach 1:
The substrate system is segmented into multiple functional layers: a sapphire substrate for ease of manufacture, a buffer layer to reduce dislocation density, and a GaN layer for high-quality epitaxial growth. This segmentation allows each layer to optimize its specific function while mitigating the overall system's disadvantages.
Solution Approach 2:
A buffer layer is introduced as an intermediary between the sapphire substrate and the GaN epitaxial layer. This intermediate layer acts as a transition zone that reduces the lattice mismatch and thermal stress, thereby lowering dislocation density and improving GaN crystal quality while still allowing the use of readily available sapphire substrates.
2Ease of manufacture
If sapphire substrate is used, then the substrate is insulating with high electrical resistivity, but this makes it unsuitable for forming devices with vertical structures and reduces effective lighting area
Solution Approach 1:
The substrate system is divided into functional segments where the sapphire substrate provides mechanical support and thermal management, while separate conductive layers are introduced to provide the necessary electrical pathways for vertical structure devices, thus decoupling the insulating property from the electrical functionality.
Solution Approach 2:
Conductive buffer layers or transition layers are introduced as intermediaries between the insulating sapphire substrate and the active GaN device structures. These intermediate conductive layers enable vertical structure formation and maintain effective lighting area while the sapphire substrate retains its insulating and mechanical support functions.
3Ease of manufacture
If sapphire substrate is used, then the substrate is readily available, but its poor thermal conductivity significantly affects performances of GaN-based devices especially large-area and high-power devices
Solution Approach 1:
The substrate system is segmented into a sapphire substrate for mechanical support and thermal management, with separate heat dissipation structures such as heat sinks or thermally conductive layers integrated into the device architecture, allowing the sapphire to provide structural benefits while dedicated thermal pathways handle heat dissipation.
Solution Approach 2:
Thermally conductive intermediate layers or heat dissipation structures are introduced between the GaN active layers and the sapphire substrate. These intermediate thermal pathways act as mediators that efficiently conduct heat away from the active regions, compensating for the sapphire's poor thermal conductivity while maintaining the availability and mechanical advantages of the sapphire substrate.
4Strength
If sapphire substrate is used, then the substrate has high hardness, but its lattice has a 30 degree angle relative to GaN crystal making it difficult to obtain a cleavage plane of the InGaN epitaxial layer
Solution Approach 1:
The substrate system is segmented so that the sapphire substrate provides mechanical strength and hardness, while the GaN epitaxial layer and buffer structures provide the necessary crystallographic orientation and cleavage properties. This segmentation allows each material to contribute its advantageous properties without being constrained by the other's limitations.
Solution Approach 2:
Buffer layers with specific crystallographic orientations are introduced as intermediaries between the sapphire substrate and the InGaN epitaxial layer. These intermediate buffer layers serve as transition zones that facilitate the formation of cleavage planes by providing appropriate crystallographic alignment, while the sapphire substrate maintains its hardness and structural integrity.
5Manufacturing precision
If GaN mono-crystalline substrate is used, then homoepitaxy improves the quality of epitaxially grown GaN crystal and allows vertical structures, but the high cost severely restricts its usage in LED devices
Solution Approach 1:
The substrate system is segmented into an inexpensive sapphire substrate for mechanical support and a thinner GaN layer for high-quality epitaxial growth. This segmentation allows the system to achieve homoepitaxy benefits in the GaN layer while using a low-cost sapphire substrate, thereby reducing overall cost while maintaining crystal quality.
Solution Approach 2:
A buffer layer is introduced as an intermediary that enables high-quality GaN epitaxial growth on a low-cost sapphire substrate. This intermediate layer allows the system to achieve crystal quality comparable to homoepitaxy on GaN substrates while using inexpensive sapphire, thus resolving the cost-quality trade-off.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composite substrate enhances GaN epitaxial growth quality, supports vertical structure LED devices, and reduces metal diffusion-related contamination, offering a cost-effective solution for GaN-based optoelectronic applications.
Implementation Method 1
at least a side wall of the composite substrate is cladded with a protective layer for preventing metal from diffusing
Implementation Method 2
the appearance of GaN mono-crystalline substrate, makes GaN epitaxy return to homoepitaxy, and improves the quality of epitaxially grown GaN crystal
Implementation Method 3
the good thermal conductivity of the GaN crystals allows the GaN epitaxy substrate to be used in the formation of vertical structures for LED devices
Data Source
AI summary
The present application discloses a composite substrate with a protective layer for preventing metal from diffusing, comprising: a thermally and electrically conductive layer (2) having a melting point of greater than 1000° C., and a GaN mono-crystalline layer (1) located on the thermally and electrically conductive layer (2). At least the side wall of the composite substrate is cladded with a protective layer (3) for preventing metal from diffusing. The composite substrate not only takes account of the homoepitaxy required for GaN epitaxy and improves the quality of the crystals, but also can be used directly to prepare LEDs with vertical structures and significantly reduce costs. The disclosed composite substrate effectively avoids the pollution of experimental instruments by the diffusion and volatilization of a metal material during the growth of MOCVD at high temperature.